1. Field of the Invention
The present invention relates to a braking force control system for an automotive vehicle, which can improve vehicle cornering stability by applying an appropriate braking force to a vehicle wheel during vehicle cornering.
2. Description of the Prior Art
In recent years, various braking force control systems for improving vehicle cornering stability have been developed and further put to practical use, by which an appropriate braking force can be applied to the vehicle wheel on the basis of some forces applied to the vehicle during cornering.
For instance, in the case of Japanese Published Unexamined Patent Application No. 5-24422, a technique for applying an appropriate braking force to a predetermined vehicle wheel is disclosed such that a target yaw rate is calculated on the basis of steering wheel angle and vehicle speed, and further a target braking force is calculated under due consideration of cornering power of a vehicle model (determined in accordance with various vehicle items and equations of motion) on the basis of detected loads applied to the vehicle wheels so that the actual yaw rate can become closer to the target yaw rate.
In the above-mentioned prior art technique, however, since the braking force is so controlled that the actual yaw rate may become closer to the target yaw rate obtained by calculation, in case the target yaw rate is set to an erroneous value, the braking force is determined erroneously, with the result that there exists a possibility that the vehicle can be lead into spin or drifts out. Therefore, for instance, when the driver turns the steering wheel excessively (e.g., to its full lock angle) to keep the vehicle away from an obstruction on a slippery road, there exists a problem in that such a large target yaw rate at which a stable vehicle driving cannot be attained is set.
In addition, when a braking force is applied to the vehicle wheel in such a way that the actual yaw rate become closer to the target yaw rate, there exists a possibility that the vehicle can be lead into spin or drift out.